Electromagnetic apparatus



June 20, 1944. c. T. HAYES 2,351,963

ELECTROMAGNETI 0 APPARATUS Filed March 3, 1943 5 Shasta-She 1 June 20,1944. 1'. HAYES 2,351,963

ELECTROMAGNETIC APYARATUS Filed March 3, 1943 5 Shoots-Sheet 3 June 20,1944.

c. T. HAYES,

ELECTROMAGNETIC APPARATUS Filed March 3, 1943 5 Sheets-Sheet 4 June 20,1944. c, HAYES ELECTROMAGNETIC APPARATUS 5 Sheets-Sheet 5 Filed March 3,1943 Patented June 20, 1944 ELECTROMAGNETIC APPARATUS Charles T. Hayes,York House, Worcester, England, assignor to Martin P. Winther, trustee,

Waukegan, Ill.

Application March 3, 1943, Serial No. 477,817 In Great Britain September18, 1942 17 Claims.

1 tofore possible in machines of given electrical capacities; theprovision of dynamometers of the class described in which heat energy ismore efficiently abstracted from the machines with less deleteriouseffects thereto than heretofore; and the provision of machines of theclass described which may be made in smaller sizes for higher energyabsorption ratings, and the mechanical constructions of which arerelatively simple so that they are economical to build, operate andmaintain. Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construotionQand arrangements of parts which willbe exemplified in the structures hereinafter described and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which are illustrated several ofvarious possible embodiments of the'invention,

Fig. 1 is a longitudinal section illustrating one form of the invention;

Fig. 2 is a cross-section taken on line 2- 2 of Fig. 1;

Fig. 3 is alongitudinal section illustrating an-.

other form of the invention;

Fig.4 is a vertical section taken on line 4-4 of said Fig. 3;

Fig. 5 is'a cross-section takenon line 55 of Fig. 3, showing certain airflow characteristics; Fig. 6 is a view similar to Fig. 3, butfragmentary and enlarged, and showing a modified form of coil enclosure;I

Fig. 7 is a fragmentary view similar to the lower part of Fig. 1,showing an alternative water-J I feeding construction; 'and,'

Fig. 8 is a vertical section taken on line 8-8 I of Fig. 7.

f Similar, reference'charactrs' indicate corresponding parts throughoutthe several views of the drawings.

While the invention herein is disclosed as being applied to eddy-currentdynamometers, it is to be noted that the improvements can also beapplied to eddy-current brakes, clutches, and the like of the type inwhich power is transmitted from a driving to a driven member by means ofan electromagnetic coupling. Such coupling is derived from a magneticflux circuit which emanates from one of said members and enters theother at relatively high concentration, the relative motion between thedriving and driven members causing the concentrated flux to functioninductively through eddy-currents to bring about a reactive magneticcondition for driving purposes.

In such apparatus, as is well known, the driven member may be preventedfrom rotating by suitable means while the driving member continues torotate, overcoming the resistance to rotation which is set up by theelectromagnetic coupling. The power which is developed in overcoming theresistance to rotation generates eddy currents in the'surface of thearmature ring forming one member of the machine, the heating in thearmature ring surface which is consequent upon the generation of theseeddy currents being dissipated by the circulation of air, water or otherliquid around the armature ring.

Usually the cooling systems hitherto employed for this general class ofmachines have supplied the air or cooling liquid to the surface of thearmature ring relatively remote from the surface in which the eddycurrents are generated. However, in some cases cooling has been provideddirectly on the eddy-current surface; see United States Patent No.2,334,976 of Martin P. Winther, issued November 23, 1943, forEddy-current coupling; also United States Patents 854,996 and 2,188,398.

Usually, but not necessarily, the eddy-current generation takes place onthe inner circumferential surface of the armature ring, and the coolingliquid circulates around the outer circumferential surface of thearmature ring. As a result of this construction there is a thickness ofiron or steel between the eddy-current surfac and the surface exposed tothe cooling liquid. This thickness of metal is determined byconsideration of (a) the annular area required for the passage of themagnetic flux and (b) mechanical strength, so that as a general rule theactual thickness is substantial. Now inasmuch as the eddy currentsgenerated have a frequency which is a function of the number of poles onthe one rotating member and its speed of rotation relatively to theother member, it will be seen that this frequency is of a high order andit has been found that the eddy current (and heat) generation takesplace in a thin section of the armature nearest to the rotating membercarrying the poles. For example, it has been found in some machines,that substantially 95% of the heat generated is created Within a thinlayer of metal where flux enters and is of the order of only inch or soin depth. The cooling liquid or the greater portion of it is thus spacedfrom the region in which the eddy currents (and consequently the heat)are generated, and the latter region therefore reaches a temperatureconsiderably in excess of that prevailing on the surface in contact withthe cooling liquid. The temperature gradient or difierence between the.two surfaces is considerable because the iron or steel, from which thering must necessarily be made, is relatively a poor conductor of heat.

A high temperature on one (usually the inner) surface of the ring and amuch lower temperature on the other surface is disadvantageous be cause(a) the material of the ring is subject to large and undesirabletemperature stresses; (1)) the electrical resistance of the ringincreases with temperature and reduces the eddy-current generation thuslimiting the capacity of the machine; and (c) the air gap between thedriving and driven member increases with increasing temperature andreduces the flux concentration, thus again limiting the capacity of themachine. In order to reduce these disadvantages to reasonableproportions it has hitherto been necessary to provide in the designsuflicient area on the eddy-current surface of the armature ring toensure a moderate temperature radient between hot and cool surfaces, andin consequence the whole machine becomes larger than would otherwise benecessary. Any increase in size is undesirable on grounds of cost and ofthe increased moment of inertia of rotating parts.

By means of the present invention there is obtained a constructionenabling faster abstraction of heat and enabling the eddy-currentsurface of the armature ring to be maintained at a much lowertemperature than hitherto; also practically eliminating temperaturestresses and at the same time improving the eddy-current generation. Theconstruction also enables the ring surface to be substantially reducedfor any given capacity, thus reducing size and cost.

As an illustrative example. in a machine using the older type of remotecooling, a rating of 1500 H. P. is based on the useful rate of heattransmission, but in the sam machine the possible electrical rating isactually 6000 H. P. Thus 4500 H. P. of the electrical rating arerendered useless.

Referring now more particularly to Figs. 1 and 2, the pedestals of themachine are shown at P. These carry bearings B providing a rocking mountfor the driven stator member shown generally at S. Member S according tothe present example is prevented from doing more than rocking by asuitable torque arm connected thereon at one of the pads T. This arm(not shown) is coupled with the ordinary weighing machine for obtainingthe force for computing torque, as is known.

The driving member is shown generally at D and constitutes a shaft lrotary in bearings RB within the driven member S. Keyed to the shaft 1is a magnetic rotor 2 having located on its outer peripheral surfaceflux-concentrating teeth 3 and 4. These teeth are parallel to the axisof the shaft I. Between peripheral sets of teeth 3 and 4 is a peripheralgroove G. The flux-concentrating purpose of the teeth is clear from saidpatents above-mentioned.

The stator S is preferably made in two halves 9 bolted together asindicated at A, and formed between them is a peripheral channel C inwhich are spacing lands 8 for nesting a peripherally wound exciting coil5. The toric flux field generated by this coil is shown at W. This coil5 is Waterproofed by an enclosing copper container sheath Y. The sheathallows cooling water to flow around the coil without damaging it. Theleads of the coil 5 are taken out through suitable water-protectivecopper tubing E soldered or otherwise fastened to the sheath D. Awatercooling inlet is shown at 28 and it will be understood that similarinlets may be employed around the periphery of the coil '5 if increasedWater inlet capacity is desired. As is usual with fluid connections onrocking stators, inlet 28 has a flexible lead to it from the main watersupply. This is not shown, being common.

Between the two stator halves 9, there is inserted a continuous circularbronze (non-magnetic) belt member 6 which causes the water to be guidedaround the coil space. Packing is shown at X. The water is allowed toflow out either through a single opening or a number of openings, suchas I, either at one position on the periphery or at several positions.Several positions are shown.

At numerals II and I2 are shown soft steel inserts forming eddy-currentcylinders. These are locally attached at welded end flanges 16. It is tobe understood that the cylinders may be inserted without flanges andattached, but that the flanges provide for easy removal of the cylindersshould they become damaged by erosion, corrosion or the like. To removethem it is only necessary to cut away the welded flange sections in alathe or boring mill to make the cylindric inserts removable. It is alsoto be understood that inserts may be dispensed with entirely (as shownon the second form of the invention to be described; Fig. 3) and theinner surfaces of the stator halves used directly for inductiveeddycurrent purposes. The small air gaps at l3 (Fig. 1) have a lowreluctance and they do not substantially reduce the magnetic efficiencyof the machine. Small dams I! are used on the stator beyond the ends ofthe teeth 3 and 4 of the rotor for purposes to be described.

Attached to the ends of the stator halves 9 by means of studs 23 arehollow circular headers 20. These in turn are attached to centraltrunnions 2| which are carried by said bearings B. Water outlets areindicated at 24, and baffles at 26. Labyrinth packless seals areconstituted by axial flanges IS on the opposite ends of the rotor 2. andby radial flanges l9 on the headers 20. These, along with diaphragmpartitions 2 l9, keep water out of the bearings B and RB.

When water flows radially from the openings 1 into the recess G, thewater has a tendency to be distributed around the rotor. If the rotor ismoving, which i usually the case when water is being introduced, theteeth 3, 4 pick up the water and throw it vigorously against the innersurfaces of the two eddy-current insert members II and I2, and since thewater is being forced in at inlet 28 it progresses axially toward thedischarge headers 20 at the ends, as shown by the of all of thedischarge.

from reaching the shaft of the machine.

arrows. 'I'he teeth '3 and 4 'act 8.812.115 causing the water to beslung out radially and maintained on the inner eddy-current surfaces ofthe stator. The dams such as I1 mentioned as being at the outer ends ofthe eddy-current rings II and I2 assure a substantially continuous depthof water film on the inner surface of II and I2, which is of a more orless uniform depth. Since the dams are low the water is spread out as athin film. The ends of the teeth 3, 4 dip into this film and I drag thewater around the periphery of II and I ature is highest.

The headers 20 carry water from the top of the machine periphery aroundthe machine to the bottom where the water outlets 24 take care Theflanges I8 have a tendency to throw the water outward and to prevent thewater from accumulating to a great depth at flanges I 9. This preventsany water Diaphragms 290 act principally as vacuum guards for bearings Rand RB.

Figs. 7 and 8 show a construction of the belt member 6 which deliverswater closer into the center of the machine. It will be seen from Fi 1that the innermost diameter of the member 6 is necessarily larger thanthe outermost 'diameteron the teeth 3 and 4 of the rotor 2.

This i for assembly purposes. In Figs. '7 and 8, a belt member 92 isused, having inwardly reaching nozzles 93 which are small enough to beintroduced between spaces between adjacent teeth on the rotor, as isclear from Fig. 8. The holes Y in the nozzles are shown at 94. Theadvantage In this form,water is introduced at one end and carriedthrough the entire gap of the machine. The stator S is composed of twocircular sections 43 including lands I0, I4, I and 2| for thefluxexciting coil 45. These lands may be integral with halves 43 orwelded on, if desired. The coil in this case is air cooled, an air inletbeing shown at 41. This inlet is somewhat larger than the nozzle 49 ofan air blower 5I. Air is directed into the opening 41 fromthe nozzle 49.The freedom between 41 and 59 allows for the required swinging orrocking movement of the stator S. A baflle 53 is inserted beneath thecoil 45 and over nozzle 49 so that the air immediately divides and flowsthrough the passages around the coil 45 around opposite sides of themachine. It

then passes to the outlet 30. Fig. 5 shows this caused to-flow in at aninlet 220 of one circular stator header 52. The flow divides at baflle95 and follows the circular header channel H5 and then over a circulardam IIG, then through an air gap H8 and across the entire machine to theopposite end where the water is discharged into channel I21 of acircular stator header 55. It flows then to the lower portion of themachine to be discharged from an outlet I26.

The circular dam H6 is important because the water is brought intocontact with the rotor 2 at a short radius and hence the water ispositively forced outwardly toward the inner stator surface H9 andacross the machine toward the outlet chamber I21. When the velocity ofthe rotor 2 reaches any substantial rate, the Water entering at 220 ismore or less uniformly distributed throughout the circular inlet chamberII5, so that the water has a tendency to overflow the dam IIBsubstantially throughout the entire periphery of the machine, and thereis no special tendency for the water to enter gap I I8 only at thebottom of the machine. In short, the rotor 2 compels the water to form acylindric ring around the entire machine. It is to be understood thatthe circular dams, although providing a difference in head, can bedispensed with by supplying adequate water pressure at inlet 220.

Water seals shown at 34 on a guard I40 prevents the water from flowingdown into the inside of the machine and resulting circular chamber I90conducts any water into the circular chamber I21. Excess is led down tothe bottom 280 of chamber I00 where centrifugal force carries it intothe lower part of the ring I21 for final discharge at outlet I26.

It is to be noted that the rotor teeth 90 in Fig. 3 are continuousthroughout the length of drum 2, and that they are extended as at at theoutlet end to form endwise extension blades I 28 which serve to directwater into the chamber I21 over an edge I29 of header 55. Inside theedge I29 the rotor is provided with a sealing rim extension I32.

Diaphragms 290 on opposite ends are principally vacuum guards for thelubricating chambers around the rotor bearings RB. It is to beunderstood that the guard I40 and water seals 34 may, if necessary, alsobe duplicated at the left-hand side of the machine to take care in somedesigns of any spill in the water entering from the chamber H5.

The headers 52 and 55 of Fig. 3, or 20 of Fig. l, which contain thewater channels, may be made of non-magnetic material, such as brass orbronze, or non-magnetic iron, if desired. This use of non-magneticmaterial increases the magnetic efficiency of the machine.

It is clear from Fig. 3 that trunnions 2I0 borne in the bearings B formthe support for the entire stator S, and the driving shaft I the support(in bearings RB )for the rotor 2. Pedestals P again carry the bearingsB. A choice of pads T is again provided for the torque transmissionapparatus (not shown) to the weighing scales (also not shown). v

As stated, the coil 45 is isolated from the water by means of thespecial lands I0 and I4 which, as shown, are integrally cast with thesteel stator halves 43, but which may be welded in place. Although theintroduction of these elements in the form of steel will cause somemagnetic inefliciency, they are made thin enough so that they becomemagnetically saturated. However, in case higher magnetic efliciency isdesired, the non-magnetic band such as the bronze shown in 2 ll (Fig.6') may be inserted between the two stator halves in slots in the bottomof which packing 44 is inserted so as to produce a seal against entranceof water to the coil. While the recess thus formed in the periphery ofthe:v

teeth, to make two sets as indicated at 9| (Fig. 6')

If desired, this feature may also be used opposite the lands Ill and Min the form of the invention shown in Fig. 3, if these be welded in arecess.

It is intended that the rate of water flow be such that the ends of theteeth on the rotor barely dip into the centrifugally formed cylinder ofwater on the interior eddy-current surfaces of the rotor. To this endthe water outlets such as 24 (Fig. 1) and I26 (Fig. 3), as indicated inthe drawings are disposed below the level of the substantially lowermostportions of the smooth flux receiving surface of the stator, whichprevents building up of any substantial bulk of water in the statorbeyond the film determined by the fiow rate and the sweep of the rotorteeth. This avoids filling the spaces between rotor teeth and avoids theconsequent unmeasured energy losses. It is of course clear thatin bothforms of the invention water is brought to the-space between the rotorand the stator by means of a circular header which ensures properperipheral distribution as the cooling space is entered. In thisconnection the space around coil in Fig. 1 may be consideredto be aninlet header. Also the heated water is taken off by a circular headerwhich relieves the space at all peripheral points.

The torque effect of the water on the machine is very small because onlythe very tips of the rotor teeth are allowed to dip into the film ofwater which covers the stator eddy-current surface. When high peripheralvelocities are arrived at, the water torque effect becomes fairlyconstant, that is, does not change with more increase in speed. Hence,although the water contributes to the torque of the machine, it is arelatively stable and constant part of its performance. In this respectthe form of the invention shown in Figs. 1 and '7 is preferable to thatof Fig. 3, because the axial length of a given pass of water through themachine is shorter than a given pass in Fig. 3. This is due to the splitpassages in Fig. 1, resulting in the length of each cylindric filmv ofwaterbeing less than its diameter. The advantage of this will appearfrom the following:

Any given cylindric film of water which is positioned on the inside ofthe outer cylindric mem ber should be equal in depth throughout itsaxial length as it is possible to obtain, so that the rotor teeth willdip into it equally throughout the lengths of the teeth.

However, it requires some difference in depth of a given cylindric filmbetween its inlet region and the outlet region in order to obtain ahydraulic head which will produce the hydraulic gradient necessary toforce it to flow axially. The longer the axial distance that the watermust travel the greater will be the hydraulic head required, and hencethe greater will be the difference between the liquid depth near theinlet region compared to its depth near the outlet region. Thus ashorter axial passage of a given cylindric film minimizes the requireddifference in film depth between its ends, and hence minimizesinequalities of the dipping depth of each rotor tooth from one end ofthe tooth to the other. It

is very desirable that a tooth at no point be dipped too deeply into theWater film, otherwise hydraulie churning and surging action increases.

As indicated in Fig. l the axial length of each water passage betweenthe rotor andstator, re-

changes in torque due to the slowness with which heat is transferredthrough the iron. This is due to the fact that the eddy-currentresistance of the iron changes with the temperature. When the resistanceto the passage of eddy currents rises, the currents drop in value, andsince the torque is proportional to the strength of the eddycurrents,the torque will drop oif when the iron becomes hot and will increasewhen the iron becomes cold. The seriousness of this type ofperformance'can be realized from the following example.

If an aircraft engine is running'at a moderately low speed, thehorsepower being absorbedby the dynamometer is relatively low, and if arapid increase in speed and power is desired, as is common in theaircraft engine industry for testing purposes and particularly tosimulate-the socalled take-off tests, it is apparent that the heating inthe iron suddenly rises very rapidly. If temperature responsive valvesare .used for increasing the water supply, there is some lag in spite ofeverything that can be done in the open ing of the valves, to supplymore water. Meantime, the iron becomes hot and the torque absorbed dropsoff. When the inrush of colder water finally reaches the iron, anadditional time is required for the heat to be transferred to the colderwater, and after a considerable time period has elapsed the torquesuddenly increases.

Furthermore, in tests at constant speeds, the same difficulty is metwithdue to an oscillating effect of torque results with the opening and.closing of water control valves. The difficulty has caused added expensefor extra equipment required to counteract it.

With the new type of cooling herein described, the dynamometer rotorliterally acts asa circulating pump supplying water directly to theheated surfaces. Furthermore, the rotor of the dynamometer imparts ahigh velocity to the water so that ideal cooling conditions areobtained. Also, some of the energy of the engine is used in circulatingthe water, and at the same time the torque required to do this isregistered on the scales.

The total volume of water moving peripherally around the machine at anyone instant is less than the total of volume spreadaround through thechannels of the older type cooling rings. Since the total volume ofwater to be heated at any instant is much less than in the older style,and it is spread out in a flatter sheet or film, the temperaturetransfer is substantially faster (in fact almost instantaneous) andtherefore the temperature of the iron does not vary so much as it doesin the older types of machines.

Thus, high velocity and quick transfer of the water across the surfaceof the dynamometer is obtained, and since the water is in direct contactwith the heated surface in which eddy-currents are generated, the oldoscillations in torque are eliminated or at least reduced. This is anadvantage from the standpoint of accuracy of testing, as well as fromthe standpoint of economy.

It has also been found that with the new sys tem the iron is kept cooleron the average of the order of 50 to 200 F. than on the'older systems,due to the intimate contact of water with the hot increased over theaverage torque available from the older type by as much as from to 30%.

Therefore, this raises the capacity of the machine 10 surface. Theaverage torque of the machine is v cylindric interior of the stator toprovide a gap for concentrated flux, a peripheral field coil carried bythe stator providing a flux field interlinking the rotor and stator, andmeans for circulating a cooling liquid around said coil and thencethrough the flux gap between the rotor and the stator.

55. In a dynamometer, a hollow stator having an interior eddy-currentsurface in cyllndric form, a solid rotor therein having exteriorflux-concentrating teeth spaced from said interior surface higher powersthan are now possible. In fact'the horsepower capacity of a dynamometerof given dimensions and weight can substantially be doubled over theoldersizes.

In view of the above, it will be seen that the several objects of theinvention are achieved and otheriadvantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shallbe interpretedas illustrative and not in a lirnitm n Iclaim:

and inner relatively rotary coaxial'cylindric mag netic members, theouter one of which is hollow and'the inner one solid; means forgenerating a magnetic field and linking said members, the, hollow memberhaving a smooth flux-receiving sur-' face and the solid member ,aflux-concentrating toothed surface, whereby heat is generated at thesmooth surface, and meansfor circulating liquid between said members andin contact with the flux-receiving surface comprising at least' oneinlet for the circulating liquid and at least one outlet therefordisposed below the level of the substantially lowermost portions of saidsmooth flux receiving surface, saidliqu'id being supplied. at such arate as to maintain on'thefsmooth su'r-i face'a cylindric film by rotarycentrifugal acac a thereon of the toothed surface, said film havinga'discrete surface adjacent'to thefend's of the teeth on thetoothedsurface.

2. In apparatus of theclass described, relatively: rotary interior andexterior magnetic members, a field coil mounted on one of said membersand providing a magnetic field interlinkin'g said members, one of themembers having fiux-concentrat ing means adjacent the other, saidmembers where adjacent providing a magnetic gap therebetween, andchannel means around the 'c'oil'and' around said field coil and throughsaid gap.

'3. In apparatus of the class described, rela-. tively rotary interiorand exterior ,magnetic members, a field coil mounted 'on one of saidmembers and providing'a' magnetic field interlinking said members,.oneof the members having communicating with the gap for circulatingwaterflux concentrating means adjacent the other,1said 1. In apparatus of theclassdescribed, outer whereby a flux gap is formed for fluxconcentrations from said teeth, said teeth being formed in two beltswith non-toothed space therebetween in the rotor, a peripheral fieldcoil mounted in said stator opposite said non-toothed space, meansproviding a water channel around said coil and including connectionswith the space between the rotor and stator, outlet headers on the endsof the stator and cooperating with the rotor to form outlet passages,and means for forcing water around said coil, through said connectionsand between the rotor and the stator to said outlet headers.

6. In a dynamometer, a magnetic stator having an interior cylindrieeddy-current surface, a magnetic rotor within the stator havingnuxconcentrating teeth spaced from said' surface, a peripheral fieldcoil mountedin the stator and providing a flux field interlinking therotor and the stator through said teeth and said eddy-current surface,opposite liquid headers on the rotor and cooperating with the ends ofthe stator, means for introducing liquid between the rotor and thestator through one header and extracting said liquid through the otherheader, means providing circulating space around said coil in thestator, and air blower means for forcing air through said space forcooling the coil independently of liquid flow.

'7 In a dynamometen'a stator having an interior cylindric eddy-currentsurface, a rotor within the stator and having exteriorflux-concentrating teeth the ends of which are spaced from said surfaceto provide a gap for concentrated flux, means engendering a iiux fieldllnKlIlg said rotor and said stator through said teeth, means forintroducing cooling liquid between tne rotor and the stator at one axialpoint and abstracting it at another axial point comprising at least oneinlet for the cooling liquid and at least one outlet therefor disposedbelow the level of the substantially lowermost portions of said eddycurrent surface, said teeth acting upon the liquid to maintain asubstantially cylindric film on said eddycurrent surface, the rate offlow of said liquid being such that the film reaches little more than tothe ends of said teeth and forming a hOllOW cylinder of water having adiscrete inner surface just within the teeth ends.

8. A dynamometer comprising paired members annularly abutted to formacomposite annular stator, a rotary shaft passing axially through saidannular members, a rotor on said shaft, end closure members on thestator forming with said paired annular members a water compartmentbetween the rotor and the stator, said annular members being recessed attheir abutments, an annular coil in the recess providing a toric fiuxfield interlinking the rotor and the stator and passing through the.water in the compartment,

9. A dynamometer comprising individual paired members annularly abuttedto form a composite annular stator, a rotary shaft passing axiallysubstantially water-protected coil compartment between said annularmembers. a

10. A dynamometer comprising paired members annularly abutted to form acomposite annular stator, a rotary shaft passing axially through saidannular stator, a rotor on said shaft, end closure members on the statorforming with the annular. members a water compartment between the rotorand the stator, said annular members being recessed at their abutments,an annular coil in the recess providing a toric flux field interlinkingthe rotor and the stator and passing through the water in thecompartment, a separate annular member within said recess andhavingwater-tight connections with the adjacent annular stator membersthus providin an annular substantially water-protected coilcompartmentbetween said.

annular members and the outside of the water compartment.

11. A dynamometer comprising paired members annularly abutted to form acomposite annular stator, a rotary shaft passing axially through saidannular members, a rotor on said shaft, end closure members on thestator forming with said paired annular members a water compartmentbetween the rotor and the stator, said annular members being recessed attheir abutments, an

annular coil in the recess providing a toric fiux field interlinking therotor and the stator and passing through the water in the compartment,and an annular coil segregating means located between said annularmembers within the recess to form an annular compartment for the coilsegregated from said water compartment, said coil segregating meansbeing non-magnetic. I

12. A dynamometer comprising a cylindric stator, a rotor located withinthe stator, one of said members having a smooth cylindric surface andthe other a polar surface, means providing a flux field linking saidmembers, end members attached to the stator, water seals between saidend members and the rotary parts providing an enclosed cylindric waterspace between the rotor and the stator, the rotor and stator beingshaped to provide an axially flowing mere cylindric sheet of wateradjacent to the periphery of said stator, water inlet means guidingwater directly to said peripheral sheet at such a rate as to maintainthe sheet form of said cylindric sheet of water, and water outlet meansdisposed below the level of the substantially lowermost portions of saidsmooth cylindric surface.

13. A dynamometer comprising a cylindric stator member, a rotary shaftpassing axially through the stator, a rotor member attached to the shaftand located within the stator, one of said members having a smoothcylindric eddycurrent surface and the other a polar surface, meansproviding a fiux field linking said members, end members attached to thestator, water seals between said end members and peripheral portions ofthe stator ends spaced outwardly from the shaft, thus providing anenclosed water space between the rotor and the stator, inlet means forbringing water directly to said water space, the water remaining in saidspace until removed from the machine, the rate of fiow of the waterbeing controlled and the rotor being shaped to provide in view of itsrotation a mere cylinder of water adjacent its periphery in flowing frominterlinking the rotor and the stator, and enclo-' sures on the statorcooperating with the rotor and having water outlets, and means forintroducing water into the space between the rotor and the stator at apoint between said end members,

15. A dynamometer comprising a cylindric' magnetic stator, a magneticrotor within the stator, one of said members having flux-concentratingmeans thereon, an. annular field coil carried in the stator andproviding a toric flux 'field interlinking the rotor and the stator, andenclosures on the stator cooperating with therotor and having wateroutlets, and means for introducing water into the space between the""rotor and the stator at a point between said endj'members for split flowbetween the rotor and the stator to the end members respectively.

16. Apparatus of the class described, comprising a hollow cylindricinductive member having aninside surface, a polar field member providingflux-concentrating surfaces near the inner surface of the cylindricmember, means providing a flux field inter-linking said members throughthe inside and the flux-concentrating surfaces, said cylindric andpolarmembers being relatively rotary and adapted to be coupledmagnetically thereby causing said inside cylindric surface to be heated,inlet means for introducing a cooling liquid at one axial point on saidhollow cylindric surface, said relative rotary movement between saidcylindric and polar member causingi said' cooling liquid to becentrifugally forced against said cylindric surface, and means forescape of said liquid from said cylindric surface fromjia second axialpoint thereon, outlet means f rreceiving liquid from said second axialpoint, said outlet means being disposed below the level of thesubstantially lowermost portions of said cylindric surface, the rate ofintroduction of thecooling' liquid being such that, in view of saidoutlet loc'a-' tion, only a thin cylinder of liquid is maintained on thecylindric surface of a depth permitting 'at most only a superficialdipping therein of'the polar parts of the polar member, the axial lengthof the liquid cylinder being less than its diameter.

17. Apparatus of the class described, comprising a hollow cylindricinductive member having an inside surface, a polar field memberproviding flux-concentrating surfaces near the inner surface of thecylindric member, means providing a flux field inter-linking saidmembers through the inside and the flux-concentrating surfaces, saidcylindric and polar members being relatively ro-' tary" and adapted tobe coupled magnetically thereby causing said 'inside'cylindric surface,to

be heated, inlet means for introducing a cooling liquid at one axialpoint on said hollow cylindric surface, said relative rotary movementbetween said cylindric and polar members causing said cooling liquid tobe centrifugally forced against said cylindric surface, and means forescape of said liquid from said cylindric surface from a second axialpoint thereon, outlet means for receiving liquid from said second axialpoint, said outlet means being disposed below the level of thesubstantially lowermost portions of said cylindric surface, the rate ofintroduction of the cooling liquid being such that, in view of saidoutlet location, only a thin cylinder of liquid is maintained on thecylindric surface of a depth permitting at most only a superficialdipping therein of the polar parts of the polar member.

CHARLES T. HAYES.

CERTIFI GATE 0F CORREC'I'I ON Patent No. 2,5 1,965. June 20, 19kb,.

CHARLES '1. HAYES.

It is hereby certified that error appears in the printed specific tionof the above numbered patent requiring correction as follows: In theheading to the printed specification, line 7, for "In Great BritainSeptember 18, 191.;2" read -In Great Britain September 8, l9L .2--; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and-sealed this Zhth day of April, A. D. 1915 Leslie Frazer(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,351,963. June 20, 191m.

crmnms 1'. HAYES.

It is hereby certified that error appears in the printed specific tionof the above numbered patent requiring correction as follows: In theheading to the printed specification, line 7, for "In Great BritainSeptember 18, 19142" read --In Great Britain September 8, 19h2--; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and-sealed this 21mm day of April, A. D. 1915.

Leslie Frazer (Seal) Acting Commissioner of Patents.

